In military ordnance arts, destructive devices known as warhead delivery systems, and commonly referred to as simply "warheads," have been developed to accomplish a wide variety of military mission requirements.
A warhead generally refers to a combination of components including, among others, a projectile designed to destroy a target upon impact, an explosive material or charge, a firing means or explosive mechanism intended to detonate the explosive charge and thereby forcibly propel or launch the projectile toward a target, a warhead housing by which the projectile and explosive charge are self contained before firing, and a launch tube for generally holding the warhead housing or canister. A delivery vehicle commonly carries the warhead to an area near or over the target.
The projectiles of the warhead may be of several types including, among others, explosive projectiles containing an explosive charge that detonates upon impact with a target, and explosively formed penetrator (EFP) warheads having warhead kill mechanisms in the form of, for example, multiple fragments, a stretched rod EFP, and an aerostable EFP. A multiple fragment EFP warhead consists of multiple and relatively small individual projectiles fired concurrently from a warhead, and is particularly suited for destruction in shotgun-like fashion of multiple targets in proximity to each other, such as enemy missiles housed on a launch platform. A stretched rod EFP and an aerostable EFP type of warhead are particularly suited for destruction of single targets that have substantial defensive capability, e.g., enemy tanks with heavy armor plating. This is so since a stretched rod or aerostable EFP is a singular projectile warhead capable of piercing through such plating.
An aerostable EFP, specifically, is a projectile that is explosively formed from a generally preformed disk-shaped member, commonly referred to as the liner. The liner is adapted to conform to the lateral cross section of a housing or canister, and also serves as an end cap for the explosive charge within the housing. Immediately after firing, however, the liner is advantageously deformed by a shock wave or expanding combustion gas impact of the detonated explosive charge within the housing, and, in turn, the liner becomes relatively axially elongated as it exits the housing. The elongation becomes conical in appearance as particularly illustrated in FIG. 9. That is, the resulting aerostable EFP projectile progressively has a widening diameter from its forward or nose end to its rearward or tail end. Such post-firing conical shaping is advantageous because the aerostable EFP projectile becomes relatively aerodynamically stable, as its name implies, and is constructed to have flight characteristics similar to that of a rifle bullet.
EFP warhead delivery systems are generally secured in place in a launch tube of a the warhead delivery vehicle such that the exit end of the warhead housing and launch tube, i.e., the end where the EFP projectile exits, is generally very proximate to a projectile exit aperture in the outer skin surface of the warhead delivery vehicle. However, warhead delivery systems are generally required to survive in hostile environments, and be capable of performing their destructive mission roles completely and with a high degree of accuracy. To this end, warheads carried aboard delivery vehicles, such as cruise missiles and the like, are designed to be sheltered or protected from detection and destruction by enemy defense systems.
Accordingly, integration of the EFP warhead into the warhead delivery vehicle often requires that the warhead shoot through an aerodynamic warhead covering device. The covering device is commonly configured to fill the projectile exit aperture and have an outer surface that conforms to the outer skin surface of the delivery vehicle. This is so that the aerodynamic stability of the warhead delivery vehicle is maintained, and secondarily diminishes detection by the enemy defense systems. These EFP warhead covering devices are commonly referred to as shoot-through aerodynamic covers. They have often been constructed of a rigid material, such as a frangible plastic material or the like, that has an adverse affect on the EFP projectile formation as the liner impacts the cover as will be described in further detail below.
In use, a selected EFP warhead projectile (for example, a single stretched rod EFP or aerostable EFP) is fired or shot from the associated housing, and breaks through the shoot-through cover that had been protecting it. The shoot-through cover is designed to readily break apart upon impact by the projectile as the projectile exits the housing. Unfortunately, however, the shoot-through cover often degrades the intended EFP projectile's shape formation and performance as compared to the shape formation without shooting through the shoot-through cover. This is thought to be caused by random fracturing of the EFP "first formed" or "forming" projectile as it impacts the cover and passes therethrough. This is due, in part, to a loss of momentum experienced by the projectile immediately after firing when it contacts the cover, and to aerodynamic instability as the impact of the projectile with the cover displaces the resulting projectile from its intended flight path.
In the case of an aerostable EFP, for example, the impact of the first formed or "forming" projectile onto the cover commonly causes the resulting or exiting EFP projectile to exhibit aerodynamic stability degradation, and may also degrade the intended flight path. Furthermore, as is the case for an aerostable EFP, the resulting projectile is designed to develop fins at its rearward end due to liner deformation through combustion gas impact, after becoming conically elongated, as aforementioned. As will be appreciated by those skilled in the art, the fins function much like fixed stabilizing control surfaces on the delivery vehicle to provide aerodynamic stability. However, it has been observed that shoot-through covers of the prior art detrimentally disrupt the fin formation because of the impact of the first formed projectile with the cover. This is illustrated in FIG. 9 by the rough or jagged peripheral end of the aft section of the projectile.
In order to obviate the detrimental effects of the so called shoot-through covering devices, some warhead covers are first destroyed by a pyrotechnic device just before the warhead is detonated, and the EFP projectile passes through the projectile exit aperture. Unfortunately, such pre-removal covering devices generally add significant complexity and cost to the warhead vehicle delivery system.
Consequently, there is a need for a shoot-through cover that tends not to degrade the aerodynamic stability of the aerostable EFP projectile, and that does not add complexity and cost to the warhead. Furthermore, there is a need for a shoot-through cover that may positively affect the resulting EFP projectile formation.